Question

In an electron diffraction tube, why does increasing the accelerating voltage decrease the radius of the diffraction rings?

Answer 1

Increasing the accelerating voltage increases the electrons’ kinetic energy and momentum, so their de Broglie wavelength decreases: \[\lambda = \frac{h}{\sqrt{2m_{e}eV}}\]. From the diffraction condition, a smaller wavelength gives a smaller diffraction angle. Consequently, the rings formed on the screen have smaller radii.